If the citric acid content is too high, it will definitely sting and have no effect. Whitening is also impossible. VC whitening can only be done after refining and stabilizing. Lemon has a high VC content, but macromolecules will not be absorbed by the skin. Unstable VC will turn black when it is decomposed by light. You might as well buy a new VC of Yangshengtang after drinking lemonade. It's very stable and won't turn black.
hope this helps